netdev - Re: [RFC bpf-next 3/7] bpf: implement devtx hook points

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Date: Tue, 13 Jun 2023 16:54:23 +0200
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Stanislav Fomichev <sdf@...gle.com>
Cc: bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net, 
	andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org, yhs@...com, 
	john.fastabend@...il.com, kpsingh@...nel.org, haoluo@...gle.com, 
	jolsa@...nel.org, netdev@...r.kernel.org
Subject: Re: [RFC bpf-next 3/7] bpf: implement devtx hook points

On Mon, Jun 12, 2023 at 7:24 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> devtx is a lightweight set of hooks before and after packet transmission.
> The hook is supposed to work for both skb and xdp paths by exposing
> a light-weight packet wrapper via devtx_frame (header portion + frags).
>
> devtx is implemented as a tracing program which has access to the
> XDP-metadata-like kfuncs. The initial set of kfuncs is implemented
> in the next patch, but the idea is similar to XDP metadata:
> the kfuncs have netdev-specific implementation, but common
> interface. Upon loading, the kfuncs are resolved to direct
> calls against per-netdev implementation. This can be achieved
> by marking devtx-tracing programs as dev-bound (largely
> reusing xdp-dev-bound program infrastructure).
>
> Attachment and detachment is implemented via syscall BPF program
> by calling bpf_devtx_sb_attach (attach to tx-submission)
> or bpf_devtx_cp_attach (attach to tx completion). Right now,
> the attachment does not return a link and doesn't support
> multiple programs. I plan to switch to Daniel's bpf_mprog infra
> once it's available.
>
> Cc: netdev@...r.kernel.org
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>


> @@ -2238,6 +2238,8 @@ struct net_device {
>         unsigned int            real_num_rx_queues;
>
>         struct bpf_prog __rcu   *xdp_prog;
> +       struct bpf_prog __rcu   *devtx_sb;
> +       struct bpf_prog __rcu   *devtx_cp;

nit/subjective: non-obvious two letter acronyms are nr. How about tx
and txc (or txcomp)

> +static int __bpf_devtx_attach(struct net_device *netdev, int prog_fd,
> +                             const char *attach_func_name, struct bpf_prog **pprog)
> +{
> +       struct bpf_prog *prog;
> +       int ret = 0;
> +
> +       if (prog_fd < 0)
> +               return __bpf_devtx_detach(netdev, pprog);
> +
> +       if (*pprog)
> +               return -EBUSY;
> +
> +       prog = bpf_prog_get(prog_fd);
> +       if (IS_ERR(prog))
> +               return PTR_ERR(prog);
> +
> +       if (prog->type != BPF_PROG_TYPE_TRACING ||
> +           prog->expected_attach_type != BPF_TRACE_FENTRY ||
> +           !bpf_prog_is_dev_bound(prog->aux) ||
> +           !bpf_offload_dev_match(prog, netdev) ||
> +           strcmp(prog->aux->attach_func_name, attach_func_name)) {
> +               bpf_prog_put(prog);
> +               return -EINVAL;
> +       }
> +
> +       *pprog = prog;
> +       static_branch_inc(&devtx_enabled);
> +
> +       return ret;

nit: just return 0, no variable needed

> +}
> +
> +__diag_push();
> +__diag_ignore_all("-Wmissing-prototypes",
> +                 "Global functions as their definitions will be in vmlinux BTF");
> +
> +/**
> + * bpf_devtx_sb_attach - Attach devtx 'packet submit' program
> + * @ifindex: netdev interface index.
> + * @prog_fd: BPF program file descriptor.
> + *
> + * Return:
> + * * Returns 0 on success or ``-errno`` on error.
> + */
> +__bpf_kfunc int bpf_devtx_sb_attach(int ifindex, int prog_fd)
> +{
> +       struct net_device *netdev;
> +       int ret;
> +
> +       netdev = dev_get_by_index(current->nsproxy->net_ns, ifindex);
> +       if (!netdev)
> +               return -EINVAL;
> +
> +       mutex_lock(&devtx_attach_lock);
> +       ret = __bpf_devtx_attach(netdev, prog_fd, "devtx_sb", &netdev->devtx_sb);
> +       mutex_unlock(&devtx_attach_lock);
> +
> +       dev_put(netdev);
> +
> +       return ret;
> +}
> +
> +/**
> + * bpf_devtx_cp_attach - Attach devtx 'packet complete' program
> + * @ifindex: netdev interface index.
> + * @prog_fd: BPF program file descriptor.
> + *
> + * Return:
> + * * Returns 0 on success or ``-errno`` on error.
> + */
> +__bpf_kfunc int bpf_devtx_cp_attach(int ifindex, int prog_fd)
> +{
> +       struct net_device *netdev;
> +       int ret;
> +
> +       netdev = dev_get_by_index(current->nsproxy->net_ns, ifindex);
> +       if (!netdev)
> +               return -EINVAL;
> +
> +       mutex_lock(&devtx_attach_lock);
> +       ret = __bpf_devtx_attach(netdev, prog_fd, "devtx_cp", &netdev->devtx_cp);
> +       mutex_unlock(&devtx_attach_lock);
> +
> +       dev_put(netdev);
> +
> +       return ret;
> +}

These two functions are near duplicates, aside from the arguments to
their inner call to __bpf_devtx_attach. Can be dedup-ed further?